Borohydride and bating treatment of hides



United States Patent ABSTRACT OF THE DISCLOSURE Applicant removes fine hair from cattle, calf, goat and sheep hides by impregnating said hides and skins with an aqueous solution of a borohydride at a pH above 9.5.

The present invention relates to a process for tanning hides, such as the hides of cattle, calves, goats, and sheep, to form high quality, full grain leather. More particularly, the invention relates to a method for removing fine hair from the hides in such a tanning process where it is desired that the hair be not severely degraded but be recovered as a by-product for other uses.

In the tanning process to which the present invention relates, as practiced prior to the present invention, the following sequence of operations were used:

(1) The raw hides were cut down the center to form two equal halves;

(2) The half hides sodium carbonate or amines, together with sodium sulfide or other reducing agent, such as sodium dithionite or other organic or inorganic sulfur compounds to loosen the hair;

(3) The hides were defleshed and then unhaired in machines designed for these operations;

(4) Hides having fine hair not removed by the machine were hand beamed, that is, they were hand-scraped with a sharp knife to remove this hair. This is an expensive and difficult operation and is eliminated by the method of the present invention;

(5) The hides then were washed for 30 minutes with a constant flow of fresh water;

(6) After washing the hides, they are treated with an aqueous liquor containing ammonium sulfate and an enzyme which neutralizes some of the lime or other alkaline material present and further removes the protein called elasten;

(7) The hides were then soaked or pickled in dilute sulfuric acid to remove the remaining lime or other alkaline material;

(8) The hides were then tanned overnight in chrome tanning solutions; and

(9) The tanned hides then were buffed, oiled or dyed and given final surface finishes.

In other tanning operations where the hair is not saved and hair, including the fine hair, is so completely degraded that it comes off the hides during the unhairing operation. In the tanning process to which the present invention relates, the milder chemical treatment does not suificiently penetrate the fine hairs to permit their easy mechanical removal. Consequenly, prior to the present invention it had been necessary to remove the fine hair by the expensive hand beaming operation previously referred to.

I have discovered a chemical treatment which can be applied in the processing sequence in the tanning process to which the present invention is directed which chemically changes the nature of the fine hair so that it is easily removed in the normal processing sequence, eliminates the expensive hand beaming operation and produces a very high quality, finished leather.

In its broad aspect the invention contemplates a method for removing fine hair from cattle, calf, goat or sheep hides comprising contacting the hides containing fine hair with an aqueous solution of a borohydride containing an amount of a base sufiicient to stabilize the borohydride and establish a pH greater than about 9.5 and thereafter adding an acidic material, such as ammonium sulfate, to the aqueous solution to lower its pH to between about 8.0 and 9.0 while the aqueous solution is contacting the hides.

More specifically in accordance with the method of the invention, the hides containing fine hair, such as the hides from the unhairing machines previously referred to (step 3 above), are subjected to a Washing operation in an aqueous medium, during which is added an amount of a borohydride between about 0.001 percent and about 0.02 percent by weight, preferably between about 0.002 and 0.005 percent, based upon the weight of the hides and an amount of a base, such as an alkali metal hydroxide, sufficient to establish a pH greater than about 9.5 and stabilize the borohydride. The hides are then subjected to a bating operation in the thereto sufficient bating materials, such as ammonium sulfate and an enzyme to lower the pH to between about 8.0 and 9.0. While I prefer to employ sodium borohydride, other alkali metal borohydrides as well as watersoluble quaternary ammonium borchydrides may be used. While I prefer to use sodium hydroxide as the base for stabilizing the borohydride, it is well known by those skilled in the art that other alkali metal hydroxides and other bases may be used to stabilize the borohydride.

In accordance with a preferred practice of the method of the invention, the defieshed and unhaired hides from step 3 above are placed in a large wooden drum which can contain as much as 5000 pounds of hides. Warm water at a temperature of about F. is introduced into the drum and the drum rotated to wash the hides. After base, such as sodium hydroxide, to establish an excess of unreacted borohydride remains, it will hydrolyze to release hydrogen and cause foaming as the pH drops below 9.5. I have found that if I wash out the borohydride solution after 10 to 60 minutes contact with the hides while the pH is above 9.5 and then add fresh aqueous medium by adding a borohydride is added, to-

water and the bating materials, the fine hairs are essentially unaffected. It appears critical, therefore, that the borohydride solution be in contact with the hides as the pH drops below 9.5.

Hides examined after the bating operation which have been treated in accordance with the method of the present invention show substantially less fine hair remaining on the hides as compared with those from a control run in which the borohydride treatment is omitted. Furthermore, the fine hair on hides treated in accordance with the invention appeared to be greatly loosened at the roots and any fine hair remaining after the bating and tanning operations is completely and cleanly removed by the normal light buffing operation. On the contrary, fine hair remaining on the hides which have not been treated with borohydride require a deep buffing operation after tanning to effect their removal and an open pore, poor surface, quality of leather is produced.

The invention is illustrated further by the following specific examples.

Example I 500 pounds of cattle hides which contained much fine, black hair after the unhairing operation were placed in a drum and washed with water at 90 F. for 30 minutes. Then 45 grams of NaBH, and grams of NaOH was added to the drum and agitation continued for another 15 minutes. The pH in the drum at this point was between 9.5 and 10.0. The bating material, 1.6% (NI- 50 and 0.075% Biobate-K4 enzyme was added. Some foaming occurred as the pH of the solution dropped, especially after the drum was rotated a few times. The bating continued for one hour. The hides were then removed and examined. Noticeably less fine hair remained on the hides at this point than is found in a run where the borohydride treatment is omitted. After tanning and light butting of the borohydride-treated hides, no fine hair was found and the leather was full-grained and closed-pore.

Example II 4-700 lbs. of cattle hides which had been unhaired but which contained substantial amounts of fine hair were washed with about 500 gallons of water in a drum at 90 F. for about 30 minutes. Then 50 grams of NaBI-L, and 5 grams of NaOH were dissolved in 500 cc. of water and the entire solution added to the drum containing the hides and wash water. The drum and hides were agitated for minutes (pH: 10). Then the usual bating material was added and the drum revolved a few times, stopped and opened. Only a trace of foam was noticed, indicating that almost all of the borohydride had been consumed during the treatment. pH at this point was 8.5.. The bating was continued as usual. The hides were tanned and finished as above. The finished tanned and buffed hides from this run were essentially free of fine hair and were fullgrained and the pores were closed.

I claim:

1. In a process for tanning cattle, calf, goat and sheep hides to form high quality, full grain leather, the method for removing fine hair from the hides comprising subjecting the hides containing fine hair to a washing operation in an aqueous medium, adding to the aqueous washing medium an amount of a borohydride between about 0.001 percent and about 0.02 percent by weight based upon the weight of the hides and an amount of a base sulficient to establish a pH greater than about 9.5 and thereby stabilize the borohydride, and thereafter subjecting the hides to a bating operation in said aqueous medium containing said hides in which sufficient bating materials are added to establish a pH between about 8.0 and 9.0, said borohydride being selected from the group consisting of alkali metal borohydrides and water-soluble quaternary ammonium borohydrides.

2. The method as claimed by claim 1 in which said hides are subjected to an unhairing operation prior to said washing operation, said unhairing operation including chemical treatment of the hides in an aqueous liquor containing lime and a reducing agent.

3. The method as claimed by claim 1 in which said bating materials include ammonium sulfate and enzyme.

4. The method as claimed by claim 1 in which said base is an alkali metal hydroxide.

5. The method as claimed by claim 1 in which said borohydride is an alkali metal borohydride.

6. The method as claimed by claim 2 in which said bating materials include ammonium sulfate and an enzyme.

7. The method as claimed by claim 3 in which said base is an alkali metal hydroxide.

8. The method as claimed by claim 7 in which said borohydride is an alkali metal borohydride.

9. The method as claimed by claim 6 in which said base is an alkali metal hydroxide.

10. The method as claimed by claim 8 in which said borohydride is sodium borohydride.

11. The method as claimed by claim 9 in which said borohydride is an alkali metal borohydride.

12. The method as claimed by claim 11 in which said borohydride is sodium borohydride.

References Cited UNITED STATES PATENTS 2,766,760 10/1956 Bogaty 132-7 2,983,760 5/1961 Charle et al. 8-428 3,092,888 6/ 1963 Mizell et al. 26-185 DONALD LEVY, Primary Examiner. NORMAN G. TORCHIN, Examiner. 

1. IN A PROCESS FOR TANNING CATTLE, CALF, GOAT AND SHEEP HIDES TO FORM HIGH QUALITY, FULL GRAIN LEATHER, THE METHOD FOR REMOVING FINE HAIR FROM THE HIDES COMPRISING SUBJECTING THE HIDES CONTAINING FINE HAIR TO A WASHING OPERATION IN AN AQUEOUS MEDIUM, ADDING TO THE AQUEOUS WASHING MEDIUM AN AMOUNT OF BOROHYDRIDE BETWEEN ABOUT 0.001 PERCENT AND ABOUT 0.02 PERCENT BY WEIGHT BASED UPON THE WEIGHT OF THE HIDES AND AN AMOUNT OF A BASE SUFFICIENT TO ESTABLISH A PH GREATER THAN ABOUT 9.5 AND THEREBY STABILIZE THE BOROHYDRIDE, AND THEREAFTER SUBJECTING THE HIDES TO A BATING OPERATION IN SAID AQUEOUS MEDIUM CONTAINING SAID HIDES IN WHICH SUFFICIENT BATING MATERIAL ARE ADDED TO ESTABLISH A PH BETWEEN ABOUT 8.0 AND 9.0, SAID BOROHYDRIDE BEING SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL BOROHYDRIDES AND WATER-SOLUBLE QUATERNARY AMMONIUM BOROHYDRIDES. 